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AD7839 bảng dữ liệu(PDF) 11 Page - Analog Devices |
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AD7839 bảng dữ liệu(HTML) 11 Page - Analog Devices |
11 / 12 page AD7839 –11– REV. 0 Automated Test Equipment The AD7839 is particularly suited for use in an automated test environment. Figure 21 shows the AD7839 providing the neces- sary voltages for the pin driver and the window comparator in a typical ATE pin electronics configuration. AD588s are used to provide reference voltages for the AD7839. In the configuration shown, the AD588s are configured so that the voltage at Pin 1 is 5 V greater than the voltage at Pin 9 and the voltage at Pin 15 is 5 V less than the voltage at Pin 9. AD7839* VREF(+)AB VOUTB DUTGND GH VOUTG VOUTH GND DUTGND AB *ADDITIONAL PINS OMITTED FOR CLARITY VOUTA VREF(–)AB VREF(+)GH VREF(–)GH TO TESTER WINDOW COMPARATOR VOUT DEVICE GND DEVICE GND –15V +15V PIN DRIVER AD588 0.1 F VOFFSET +15V –15V 4 6 8 13 2 16 3 1 15 14 9 AD588 +15V –15V 4 6 9 13 7 2 16 3 1 15 14 8 10 11 12 1 F DEVICE GND 10 11 12 7 1 F Figure 21. ATE Application One of the AD588s is used as a reference for DACs A and B. These DACs are used to provide high and low levels for the pin driver. The pin driver may have an associated offset. This can be nulled by applying an offset voltage to Pin 9 of the AD588. First, the code 1000 . . . 0000 is loaded into the DACA latch and the pin driver output is set to the DACA output. The VOFFSET voltage is adjusted until 0 V appears between the pin driver output and DUT GND. This causes both VREF(+) and VREF(–) to be offset with respect to GND by an amount equal to VOFFSET. However, the output of the pin driver will vary from –10 V to +10 V with respect to DUTGND as the DAC input code varies from 000 . . . 000 to 111 . . . 111. The VOFFSET voltage is also applied to the DUTGND pins. When a clear is performed on the AD7839, the output of the pin driver will be 0 V with respect to DUTGND. The other AD588 is used to provide a reference voltage for DACs G and H. These provide the reference voltages for the window comparator shown in the diagram. Note that Pin 9 of this AD588 is connected to Device GND. This causes VREF(+)GH and VREF(–)GH to be referenced to Device GND. As DAC G and DAC H input codes vary from 000 . . . 000 to 111 . . . 111, VOUTG and VOUTH vary from –10 V to +10 V with respect to Device GND. Device GND is also connected to DUTGND. When the AD7839 is cleared, VOUTG and VOUTH are cleared to 0 V with respect to Device GND. TrimDAC is a registered trademark of Analog Devices, Inc. Programmable Reference Generation for the AD7839 in an ATE Application The AD7839 is particularly suited for use in an automated test environment. The reference input for the AD7839 octal 13-bit DAC requires three differential references for the eight DACs. Programmable references may be a requirement in some ATE applications as the offset and gain errors at the output of a DAC can be adjusted by varying the voltages on the reference pins of the DAC. To trim offset errors, the DAC is loaded with the digital code 000 . . . 000 and the voltage on the VREF(–) pin is adjusted until the desired negative output voltage is obtained. To trim out gain errors, first the offset error is trimmed. Then the DAC is loaded with the code 111 . . . 111 and the voltage on the VREF(+) pin is adjusted until the desired full-scale voltage minus one LSB is obtained. It is not uncommon in ATE design, to have other circuitry at the output of the AD7839 that can have offset and gain errors of up to say ±300 mV. These offset and gain errors can be easily removed by adjusting the reference voltages of the AD7839. The AD7839 uses nominal reference values of ±5 V to achieve an output span of ±10 V. Since the AD7839 has a gain of two from the reference inputs to the DAC output, adjusting the reference voltages by ±150 mV will adjust the DAC offset and gain by ±300 mV. There are a number of suitable 8- and 10-bit DACs available that would be suitable to drive the reference inputs of the AD7839, such as the AD7804, a quad 10-bit digital-to-analog converter with serial load capabilities. The voltage output from this DAC is in the form of VBIAS ± V SWING and rail-to-rail opera- tion is achievable. The voltage reference for this DAC can be internally generated or provided externally. This DAC also contains an 8-bit SUB DAC which can be used to shift the complete transfer function of each DAC around the VBIAS point. This can be used as a fine trim on the output voltage. In this application two AD7804s are required to provide programmable reference capability for all eight DACs. One AD7804 is used to drive the VREF(+) pins and the second package used to drive the VREF(–) pins. Another suitable DAC for providing programmable reference capability is the AD8803. This is an octal 8-bit trimDAC ® and provides independent control of both the top and bottom ends of the trimDAC. This is helpful in maximizing the resolution of devices with a limited allowable voltage control range. The AD8803 has an output voltage range of GND to VDD (0 V to +5 V). To trim the VREF(+) input, the appropriate trim range on the AD8803 DAC can be set using the VREFL and VREFH pins allowing 8 bits of resolution between the two points. This will allow the VREF(+) pin to be adjusted to remove gain errors. To trim the VREF(–) voltage, some method of providing a trim voltage in the required negative voltage range is required. Nei- ther the AD7804 or the AD8803 can provide this range in nor- mal operation as their output range is 0 V to +5 V. There are two methods of producing this negative voltage. One method is to provide a positive output voltage and then to level shift that analog voltage to the required negative range. Alternatively |
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